1. Click Settings.
2. Click Virus and Spyware Protection.
3. Click File Exclusions tab.
4. Under Which disks, folders, or files to exclude from risk scanning, click New.
5. Select the folder you want to exclude and click OK.
6. Under Which disks, folders, or files to exclude from Auto-Protect scanning, click New.
7. Select the same folder that you excluded in line 5 and click OK.

This only works on Norton 360 2.0. You'll have to upgrade from any 1.3 version if you haven't.

It's not viruses that's the problem, it's the fact that the Anti-Virus program is continually checking a file that is used by TF2. TF2 updates this file frequently, and as a good antivirus program would, it checks to see if they changes are virus related.

This constant checking causes your computer to use up CPU resources that could have gone to making TF2 run smoother. So all the OP is trying to say is the list this specific folder as an exception so that the Anti-Virus program doesn't take up CPU resources checking it every minute.

Edit: Everyone, PLEASE READ the first post before spouting off nonsense about viruses! The OP did NOT mention anything about viruses at all!

Well you apparently didn't read my post. You don't need to have virus checkers running at all! Just don't be stupid and you won't get viruses and if you do which is bound to happen anyways, just run a good scanner once or twice and you should be all set.

hmm, while I'm not on the TF2 project, I'll poke around the code to see what is in this stats file, why it is being so frequently updated, etc. No promises though!

Ten pages in, and someone finally posted a touch of sanity.

While Antivirus products should only be used as training wheels, that doesn't mean that adding exclusions is acceptable procedure. If your AV is doing THAT much damage to your gaming performance, and only to this one game, then something is BROKEN.

If your FPS is consistently low without the exception in place, then that indicates some sort of very unfriendly behaviour. Either the AV process is just completely insane, or the file in question is being written to both heavily and constantly. This seems unlikely. You guys could either poke randomly at it, or bust out the tools and actually check.

If your FPS is fine mostly, but drops to zero for a few hundred milliseconds here or there, then that sounds more like a file getting written occasionally and causing the system to drop everything and scan it.

Try leaving NOD32 enabled and start the game. Monitor your FPS min, max and averages. Then disable it entirely and start the game with the same conditions.
Let us know if it makes a difference in a measurable and reproducible way.